Various types of tools require a user to selectively attach a tool accessory such as a drill or router bit. Over the course of a particular project or work period it may be necessary to employ a variety of such accessories and to replace worn or broken ones. Convenient removal and replacement of the interchangeable tool accessories is therefore desirable. Two commonly employed mechanisms for holding interchangeable accessories are chucks and collets. Collet type mechanisms are usually favored for tools with higher rotational speeds.
In a collet-type holder, the shank of a tool accessory is inserted into the bore of a collet. A collet is a generally cylindrical element with a longitudinal bore. The collet has at least one end with a plurality of longitudinally extending arcuate jaws arranged equiangularly around the circumference of the collet and spaced apart by a plurality of longitudinally extending cuts. The collet may be machined into the end of a tool output element (such as a shaft, spindle, or arbor) or it may be a separate (sometimes barrel-shaped) element.
A collet nut or collet ring is installed over the collet. The collet nut is threaded onto the end of the tool shaft or spindle. Threading the collet nut down on the spindle causes surfaces on the inside of the collet nut and/or shaft to compress the jaws of the collet around the shank of the tool accessory. Thereby securing the tool accessory to the power tool shaft/spindle.
When changing accessory tools, the nut must be loosened to allow the collet to expand and release its grip on the tool accessory. The tightening and loosening of the collet nut may be partially performed by hand, but the size and shape of the collet nut make it difficult and/or uncomfortable to properly tighten and then initially loosen the collet nut using hands alone. Therefore, it is often necessary to use a hand wrench or similar tool in order to apply sufficient torque to the collet nut.
In the case of rotary or power tools, when tightening or loosening the collet nut, the shaft/spindle must be prevented from rotating or else it would be difficult to achieve relative motion between the nut and the rotatable spindle.
Conventionally, the loosening and tightening process requires that the operator simultaneously grip both the shaft/spindle and the collet nut with two separate hand wrenches or the like. A torque is then applied to the nut while the shaft is held in place. This is an awkward process, made even more so by the necessity to support the weight of the tool itself during the process.
More recently, tools have been designed that incorporate a locking mechanism that locks the shaft/spindle relative to the tool housing. Thus, the rotation of the shaft can be prevented, simply by employing the built in shaft lock. For such a power tool, only one hand wrench is required to loosen or tighten the collet nut, as seen in U.S. Pat. Nos. 5,496,139 and 5,813,805.
The need to use even one hand tool to change tool accessories, however, is still inconvenient. For example, when a bit replacement is required, the tool operator has to stop what he is doing to find a wrench. This delay can be meaningful in jobs, such as drywall installation during major construction or remodeling projects, where high production rates are essential.